IOWA ACADEMY OF SCIENCES. 
47 
secure foundation of fact, not inference, that chemical 
energy is the only source for the energy appearing in the 
animal cell in its several kinetic forms — heat, light, 
mechanical work, electricity. 
The production of heat and light in the animal cell in- 
volves transformations most readily understood. Just as 
oxidation in a physical system other than the living trans- 
forms the potential energy of organized matter into heat, 
so, in the animal cell, heat is the direct outcome of the 
chemical transformations of dissimilation. Since light and 
heat are but different phases of the same radiant energy, 
so the basis of light- production in the cell is the same as 
for heat-production. Experimentally, the oxidation of fatty 
granules in the presence of an alkaline medium yields 
light. Special phosphorescent organs are cell-groups where 
such fatty particles, resulting from metabolism, are burned 
in an abundant supply of oxygen. It is possible that light 
is a more widespread accompaniment of cell-life than is 
usually supposed. 
The transformation of chemical energy into the mechan- 
ical energy of movement is slightly less direct, involving 
surface tension. Experimental work with oil-drops shows 
that amoeboid movement is the simplest condition and 
should be taken as the starting-point. An amoeboid cell 
has its surface unspecialized, permitting freedom of move- 
ment. With surface tension equal at all points, the form 
of such a cell must be that of a sphere. It is evident that 
a local alteration of surface tension must result in a cor- 
responding change of form at the point where alteration 
occurs. Reduction of surface tension will be expressed by 
the formation of a pseudopodium; increase of surface 
tension by its retraction. Now, the chemical changes 
occurring in living matter provide the conditions for the 
alteration of surface tension. The introduction of oxygen 
increases molecular instability, leading to the reduction of 
surface tension and the protrusion of pseudopodia; recon- 
struction of the molecule must, conversely, increase sur- 
face tension, causing the retraction of pseudopodia. Thus 
the phenomena of movement result from local differences 
